Fight Fire With Fire
by Miss Mungoe
Summary: She'd grown up the oldest of five; there was no way she was going to be bested by a cheeky brat like Roy Mustang. – Olivier's patience is tested; Roy is having the time of his life.


AN: For **mirkwoodse** on tumblr, who asked for something with Olivier and Roy. And since I don't ship it, it'll have to be reluctant friendship shenanigans. I hope you like it! Olivier and Roy butting heads, set after the series, no pairings, and rated T for the occasional cuss word. I've taken a few liberties with Roy's background, but nothing that isn't canon-compliant.

Disclaimer: Fullmetal Alchemist and its characters belong to Hiromu Arakawa; I own nothing.

* * *

**Fight Fire with Fire**

by Miss Mungoe

To be fair, he'd had a lot of foster sisters. He _knew_ how to push buttons.

The door to his office was slammed open with more force than strictly necessary, and Roy looked up from his papers as the Briggs Major General stalked up to his desk, before depositing, with a chilling glare, a heavy box that had the assorted knick-knacks scattered across it bounce and topple.

He looked at the box, then at her, and raised a brow. "Something the matter, General?"

She crossed her arms over her chest. "Your glibness does you no favours, Mustang," she snapped.

He placed the documents in his lap, and managed his best expression of innocence. "I'm afraid I don't know what you're talking about." She didn't look at the box, but it sat between them, its presence glaring like a proverbial elephant. He didn't smile, because that would ruin it. "I was under the impression women liked gifts," he said then.

She glared. "_Gifts_," she spat the word like she might have 'Drachma'.

"Yes."

She placed a hand on the box, and promptly shoved it towards him, making most of the things on his desk fall into his lap, and he jumped, hands making a futile grab for the stacks of documents fluttering to the floor around him. The Lieutenant would have his head now, after all the trouble she'd gone through to organize them. He sighed. "Was that strictly necessary?"

Her glare didn't lessen. "I might ask the same." She pushed the box again. "Trashy romance novels, Mustang?"

He smiled. "Did you like them?"

Her look darkened. "The only use for these aberrations is to light a fire."

"Ah, but you haven't," he pointed out, as he glanced into the confines of the box. Sure enough, the books were there, stacked neatly atop one another.

The fingers curled around the rim of the box tightened, and he was mildly surprised she hadn't gone for her sword yet. "The men get bored," she ground out instead. Then, and with effort, as though it physically pained her to speak the words, "They would like the sequels."

He raised a brow, and she raised one back, as though daring him to make a comment. He merely smiled. Her reputation as the commanding officer in Amestris who'd go to the greatest lengths for her men wasn't undeserved.

"I'll look into it, General."

"See that you do."

"Anything _you_ would like?"

She glared. "Your rank taken down a few notches, and your nose out of my business."

He grimaced. "That's harsh, and to someone who went through the trouble of sending you books." He looked into the box, and pulled out a well-thumbed novel.

She snorted. "I'd sooner call it firewood."

"My foster sisters love these, you know."

She raised a brow. "I was unaware you had sisters, Mustang."

He shrugged. "You've never bothered to ask, Major General."

An odd moment followed, like the drawing of a starved breath between battles, and for the span of a single second there was an _understanding_ there, between two people who knew different sides of the eternal strife that is sibling rivalry and the struggle to always one-up each other. It was a rare occurrence, like the alignment of planets, and for one moment their long upheld tug-of-war was replaced by an accord of sorts.

But of course, as with all good things, they come to an end.

"I'm surprised you grew up so uncouth, with so many women around," she snorted, before she spun on her heel, golden hair whipping about her face as she made for the door without another word.

He smirked, and called after her, "And yet surrounded by men, your feminine grace never ceases to astound me, General Armstrong. What's your secret?"

When she slammed the door this time, it was with enough force to rattle the pictures on the wall, and he heard her stomping footsteps loud as cannon-fire down the corridor of Central Headquarters. But the box still sat on his desk, and, he noted with a grin, despite her quite obvious ire she hadn't withdrawn her request.

And forever the little brother, Roy considered that a victory.

* * *

She'd only ever had one little brother, and for all his bluster, Alex had always been exceedingly polite, and had kept out of her hair when she'd demanded it. But sometime during the course of the last few years, she seemed to have gained a parasite the likes of which her _otouto_ had never even been _close_ to being.

"Roy Mustang on the phone for you, ma'am," Karley announced when she stepped into the communications office, holding out the ear-piece. "Says it's urgent."

Taking it from his hands, she barked into it, "Speak_._"

There was a noise of discontent over the line. _"How rude, General! I might have been on my deathbed, and this is how you'd greet me, about to say my final words?"_

She took a seat at the edge of the desk. "You'd be dead already, with how much you talk," she retorted. "Now spit it out, I don't have all day. And I was told this was urgent."

There was a pause. _"Where would you have wanted to dine in Central City, if I had emptied my pockets and my dignity for that dinner I never bought you?" _

She didn't know what the hell to make of that. "Are you _drunk_, Mustang?"

"_Just answer the question, General."_

She snorted. "Nowhere you could afford, but the one on the corner by the river serves the best Xing cuisine in Central." She paused. "Why are you asking?" Then she smirked. "Oho? Finally decided to man up and take a lady out the way she deserves?"

There was a pause. Then, _"Maybe." _

"And you called me to ask for _advice_?"

There was a longer pause, and she swore she could hear his grin over the phone. _"Well, I figured with your knowledge of the feminine whims–"_

She slammed the receiver down so hard Karley nearly choked on his tongue, and rose from her seat, glaring at the Communications Officer as she pushed past him on her way out. "If he ever calls again, direct him to _Drachma_," she spat as she stomped away, muttering under her breath.

Karley ran a hand through his hair, and sighed. "Gotta give him credit," he said to his fellow officer across the room, who looked like he was trying very hard to hide a grin.

"There aren't many who can rile our Queen up quite like _that_."

* * *

"What do you mean I can't wear my dress uniform? It says_ formal wear_!"

The invitation was slammed down onto his desk, toppling the inkwell and spilling ink across the papers the Lieutenant had laid out before him earlier that morning with the explicit order not to misplace. But despite the mess, and the glaring blonde, Roy offered an amicable smile. "It's not supposed to be a military event, General. After all, we're trying to tone down the whole 'military state' affair, no?"

She glared as though he'd suggested she make peace with the Drachmans. "I am not putting on a _dress_, Mustang," she all but growled. "Dress blues have been the norm in this country since I joined the military."

Roy shrugged. "That was before. Grumman felt this would make a nice change."

She visibly seethed. "That perverted old coot only wants an excuse to see the women out of uniform!"

"That may be, but the decision has been made, regardless, and the invitations are already out. I can't make exceptions, General, even for you."

She crossed her arms over her chest. "Fine. I'll schedule my return to Briggs on the morrow, then."

Roy raised a brow. "As the head of the Armstrong family, you are obligated to attend."

She waved him off. "I gave the estate to my brother, Mustang. Your argument doesn't hold shit."

"Interesting, because your brother was the one who requested your attendance."

She visibly balked. "That _little_–"

Roy grinned. "So it's settled! Will you be bringing a plus one?"

She slammed both hands down on the desk, the motion rattling the various oddities he had cluttered across it. The inkwell rolled off the desk to land on the floor. "Does my sword count?" she snarled, "Because I'll be putting it through _you_ the first chance I get."

He smiled. "Your ardent refusal surprises me, General," he said then. "And here I thought you were always up for a challenge." Her eye twitched a little at that, and he felt his smile widen. "Oho? What's this? The Northern Wall of Briggs, defeated by the prospect of wearing a _dress_?" he asked then, leaning back in his chair. "My, but what wouldn't Drachma pay for this information."

She breathed out through her nose – a tell-tale sign, if he'd learned anything from his childhood, that she was about to throw something. Luckily for him, he was pretty adept at ducking.

But all she did was glare, arms crossed over her chest and brows furrowed so sharply he wondered idly if she was thinking about places to deposit his corpse. It felt very much like a stand-off, and he watched her, genuinely interested in seeing what she would do.

She surprised him then, by squaring her shoulders. "_Fine._ I'll wear a damn dress," she declared, as though she'd just issued a declaration to duel. She pointed a finger at him, and her voice dropped dangerously, "But if you think I'm putting on heels, Mustang, I will find a pair and shove them up your ass!" Then she spun on her heel, and stalked out of the office.

He waved pleasantly at her retreating back. "I do believe that kind of language isn't very becoming of a _lady_–"

"Fuck off!"

The door slammed again, the hinges shrieking as though in physical pain, and Roy mused that he might want to get them oiled.

* * *

In retrospect, he should have known it was going to come back to bite him in the ass.

He just hadn't expected it would come in the shape of betrayal, and from his closest circle, to boot.

"Really, Roy-boy. What is this I've been hearing about your behaviour?"

His plump foster mother grinned as she leaned against the bartop, but Roy wasn't looking at her, but the person sitting at the barstool in front of her, her unadorned blonde hair and the blue of her uniform distinctly out of place and glaringly easy to spot amongst the other elegantly dressed girls seated at the bar.

With a glance over one shoulder, Olivier Armstrong smiled an unmistakably cunning smile. "_Roy-boy_," she said simply, and he marvelled silently at her ability to cram so much authority into a simple nickname.

But then he remembered, she was the eldest of five, and an Armstrong.

He sighed as he tugged off his jacket, before he went to take a seat amidst the clever smiles and grinning eyes that painted an obvious picture of what had gone down before he'd come in. It was the smiles of older sisters who'd finally gotten their due after years of cheeky behaviour and a baby brother constantly getting into their hair.

Seeing no point in beating around the bush, he accepted the cup placed before him, and directed his question at his foster mother. "What have you told her?"

Chris Mustang raised a brow. "Oh, nothing incriminating, Roy-boy. Just a few stories."

"A few stories?" He looked over at the Major General of Briggs, who shrugged much too casually.

"Just a few," she asserted. Then, "But they were quite _interesting_. My, but you were a bit of a hassle growing up." She looked at him from over the brim of her cup, blue eyes sharp like ice in the dim lamplight. He pressed his lips together as he considered her words, and the implications. It felt distinctly like a noose was being tightened around his neck.

"This information will come in handy," she declared then, as she idly considered her fingernails. "When that old pervert finally retires, and you find yourself at the head of this nation." She shot him a look. "Your formal events better include dress blues, or so help me, _Roy-boy_, your reputation will plummet faster than a cold corpse over the side of Fort Briggs."

He grimaced. "Lovely imagery, General."

She sipped her tea coolly. "I've found that graphic descriptions always make the best impressions."

He sighed, and shook his head. Then he looked at his foster mother. "I can't believe you've betrayed me like this."

She shrugged, a smile stretching along her mouth. "Don't take it personally, Roy-boy. We ladies have to stick together in this world of men." He muttered something about the Major General only calling herself a lady when it suited her own needs, but didn't let his words be heard, as he was quite thoroughly, and literally, out-manned.

"What's that saying, Mustang," the Major General asked then, tapping her finger idly against the cup in her hand. "Fight fire with fire?" She raised a brow. Roy could only sigh, but had to smile. Olivier Armstrong grinned, and drank her tea. "You're ten years too young to outwit me, brat," she declared.

"And you better not forget it."

* * *

AN: They've got such a fun dynamic in the anime, and when I got the request this thing kind of wrote itself. But then, I'll jump at any chance to write Olivier.


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